Field of the Invention
The present invention relates to a numerical controller that can continue DNC operation even if a communication failure occurs during the DNC operation.
Description of the Related Art
A numerical controller usually performs machining by using an NC program stored in a storage medium (such as a non-volatile memory and an HDD) in the numerical controller. Meanwhile, a numerical controller connected to a communication line has a function of performing machining by using an NC program supplied from a host (computer that an FTP server, an HTTP server, and the like run on) through the communication line, without saving the NC program in the storage medium, not using the NC program stored in a storage medium. Such a method of operating a machine tool while transferring the NC program through a communication line or the like is called DNC operation.
In the DNC operation, the reception of the NC program from the host and the machining of a workpiece are performed at the same time. Therefore, when a communication failure occurs in the communication line between the numerical controller and the host, the numerical controller cannot receive the NC program, and the machining is stopped in the middle. If the machining is stopped in the middle, there is a problem that a cutter mark is made on the workpiece or that a vibration is generated. The communication failure needs to be solved to restart the machining, and there is a problem that the machining time becomes long due to the time required to solve the communication failure.
Therefore, as shown in FIG. 8A, a communication unit 40 in the DNC operation sequentially stores the NC program received by communicating with a host 60, in a buffer provided in the communication unit 40. A DNC operation management unit 30 supplies the NC program stored in the buffer in the communication unit 40 to a numerical control unit 20. Providing the buffer in the communication unit 40 can avoid the stop of machining when a communication failure occurs, because the NC program stored in the buffer can be used if the communication failure is a temporary failure.
The method of preparing the buffer in the numerical controller has a certain effect on a communication failure recovered in a very short time or on a temporary communication delay. However, when the communication failure or the communication delay is prolonged, the NC program in the buffer is exhausted as shown in FIG. 8B. The DNC operation management unit 30 cannot supply the NC program to the numerical control unit 20, and as a result, there is a problem that the machining is stopped.
A DNC operation method with a function of retracting a tool in cutting operation in an axial direction of the tool installation, in order to avoid the problem that a cutter mark is made on the workpiece or that a vibration is generated due to the stop of the reception of the NC program caused by the communication failure or the like, is well known as disclosed for example in Japanese Patent Application Laid-Open No. 7-239707. However, the DNC operation method is for reducing the influence when a communication failure occurs or the like and is not for solving the problem that the machining time becomes long when the communication failure is prolonged.